CloudCompare forum

Good afternoon to all!

Currently I'm a graduate student trying to learn CloudCompare (beginner) and would need help regarding alignment of point clouds for my research. I need to look at the difference between two clouds and the change in elevation should be zero (or near zero) as these were taken a day apart.
After importing both, I manually align them with the Translate/Rotate tool, then run ICP (fine registration) with the reference being the "before" point cloud and the to be aligned being the "after" point cloud with RMS diff of 1.0E-6 and a random sampling limit of 10,000,000, while having rotation and translation with XYZ and Tx Ty Tz, respectively. Next is applying the Cloud/Cloud Dist tool (C2C) with max distance applied at 4.94 in this case, and having split X Y Z components applied.
This gives me a range of 0.00049m and 0.22m, which is a fairly large range. Furthermore, once done, these two point clouds are exported as DEMs (tools > projection > rasterize), to perform raster calculator in ArcGIS, where this gives me a mean of 0.0077m, which is fairly good, but not near zero enough.

My question is: is there a way to further reduce the range I'm getting? I would love to see a range of 0.0004m (0.4mm) and 0.001m (1mm) for example.

Any help will be greatly appreciated! Thank you in advance!

So pay attention when computing the distance in CC with the C2C distances computation tool, that the clouds density and non-overlapping parts (or holes) will have a big impact. It's better to use M3C2 for instance.

And for registration, it's a similar problem. Make sure the 'overlap' parameter is not set too high. Any mismatching parts will prevent the clouds from aligning properly. Also, a random sampling limit this high doesn't look to be useful.

Don't hesitate to share some screenshots, or even send us the clouds (admin@cloudcompare.com) if you want more support.